you have multiple address vendor address (one default address and reaming secondary address ) while create purchase order system picking by default address after select vendor account .
If you want to buy goods from secondary address with same vendor and in the PO level there is no facilities to change vendor address in system.
But you can able to change vendor address in tax information level and if you have no of line in PO you have to change vendor address manually it is consuming more time for doing this process. Instead of change vendor address in line tax information.
Firstly it can be the reason of posting wrong component of GST. Because component decide based on address selection. So legal compliance will be raise due to this or there can be multiple tax adjustment entries need to perform after reconciliation.Secondly If we have multi line PO then we need extra workforce.